The round thermostat which was originally pioneered by the assignee of this patent has become one of the most ubiquitous features of the modern home. It has been produced in a number of different versions, but all have a number of common features. These include a housing having a generally circular periphery with a central axis and a front face on which is carried a scale of the thermostat setting. For adjustment of the thermostat setting, there is a thermostat knob having an axis of rotation coinciding with the central axis. The thermostat knob has a predetermined external shape which includes a circular wall projecting from the housing. A pointer on the thermostat knob indicates the current setting on the scale. Typically, the diameter of the housing may be 70-100 mm. and the thermostat knob may be 50-60 mm. in diameter.
A version now available is intended for use by the vision impaired. This version has extra large (over 8 mm.) raised numbering on the scale, and a detent which clicks for each 2F. rotation of the thermostat knob. The temperature settings divisible by 10 have a looser detent which creates a distinguishable tactile impression compared to the detents in the other setting positions. The two types of detent allow a person with very severe vision impairment to adjust the thermostat setting by tactile sense only since it is easy to estimate within 10F. the current temperature setting from the temperature level of the room.
It is not uncommon that people who have vision impairment also have strength impairment. This circumstance may arise from old age or from diseases which affect both their strength and their vision. Because of their vision impairment, the vision-impaired model is very desirable, but their strength impairment causes them difficulty in rotating the thermostat knob of a vision-impaired version against the resistance of the detent.